JOP146 Fine Temperature and Density Structure of Coronal Loops in a
Bipolar Active Region
Authors: J. Cirtain; C. Kankelborg, P. Martens
Objective:
Observe coronal loops on the west limb with multiple
instruments. These loop(s) must originate from one bipolar region
or a region of minimum magnetic complexity.
Necessary conditions for Operation:
A relatively simple region consisting of a bipolar surface origin
is requisite for co-operation of all instruments.
Scientific Justification:
Currently, several diagnostic approaches for the determination of
the temperature stratification along loops exist, dependent upon
the observing instrument. These determinations give widely
differing results for the nature of the plasma within a coronal
loop. Aschwanden et al (ApJ 550,1036; ApJ, 550,1059; etc.) has
shown in multiple papers the nearly isothermal results obtained
through filter ratios derived from EIT and TRACE data. J. Schmelz
and others (ApJ, 556,896) have produced multi-thermal results
through the analysis of spectra obtained from CDS observations
while Acton and Priest (ApJ, 539,1002) have developed a uniform
heating model from SXT data. These separate studies have shown
that results vary depending on the instrument and subsequent
method of analysis. It is therefore of great necessity to perform
a co-operative study with all these instruments further
constraining the actual thermal gradient of coronal loops. There
have been many joint observing programs with similar
goals. However, these have yet to provide a data set that both has
a minimum of magnetic complexity, required to distinguish a unique
structure by the CDS spectrograph, and co-observation by SXT,
TRACE, CDS and EIT of a simple structure on the limb. Recently,
JOP 145 was run with SCT< CDS, TRACE and EIT. This JOP offered all
of the necessary criteria for the study except it changed target
before the structure made it to the west limb. Unfortunately,
there are many data sets but none offer that which is here
stipulated as necessary to accomplish the scientific study
suggested.
J. Schmelz has developed a Differential Emission Measure technique
applied to spectral intensity numbers from CDS observations. This
method can be modified to evaluate both the spectra from CDS and
the filter output from TRACE and SXT. By comparing the spectral
intensities from CDS with the 171 A, 195 A, and 284 A filters from
TRACE and the AlMg and Al filters from SXT, a high resolution
composite of the loop can be created that has spectral data for
the structure to further constrain the actual nature of the plasma
in both temperature stratification along the loop and fine
structure detail of the loop. This analysis method may provide the
unique ability to determine the real temperatures of plasma within
these structures as well as perform a diagnostic cross calibration
of the three instruments.
Pointing:
This program is to be executed at the solar limb thereby
minimizing projection effects and preferably targeting a region
that has been under observation as it rotates across the disk.
Operation Details:
The JOP is to be performed in the following manner on a per instrument basis:
CDS: target of opportunity with as many sequences as possible.
TRACE: observations to overlap with other instruments when target
approaches west limb. Previous observations as loop rotates across
disk are preferred.
SXT: target of opportunity only with regard to the PFI images.
The entire study will be on a target of opportunity basis for the
month of September or as instrument schedules dictate.
CDS: Three sequences to be run: O_LOOP1 and O_LOOP2.
O_LOOP1 creates a 160 x 240 arc second raster in six wavelength
bands. These bands are He 1 584.33 A, O III 599.66 A, O V 629.73
A, Ne XI 562 A, Mg IX 368.06 A and Fe XVI 360.76 A. It steps in 4
arc second increments. The exposure time at each position is 10
seconds resulting in a cadence of about ten minutes. This should
be the initial program for the CDS observation. O_LOOP2 has an
almost identical raster but it creates a raster with thirteen
wavelength bands over approximately forty minutes. The wavelengths
for this program include the six wavelengths for the O_LOOP1 run
with the addition of Si XII 520.665 A, Si X 347.40 A, Al XI 562.77
A, Fe XIV 353.92 A, Si IX 345.220 A, Si X 356.0 A and Mg X 624.817
A. This sequence is intended to supplement the O_LOOP1 program and
should only be run after the O_LOOP1 program has completed several
runs. These sequences must be run simultaneously with TRACE and
SXT. Multiple runs sequentially are preferred.
TRACE: Through the use of currently available observing programs,
specifically mostly171.utim and mostly195.utim, coverage of an
active region will be possible in 171A, 195A and 284A. These
filters correspond to spectral lines available with CDS and
provide approximate temperatures that overlap the temperatures
available in CDS and SXT. Also intermittent C IV 1550 A. runs
would be required to supplement the temperature analysis method to
be subsequently employed. The .utims that are suggested for use in
this study offer a sustainable cadence of around 40 seconds. The
mostly171.utim offers the 171 filter for the main wavelength with
195, 284, 1550, 1700 and WL every eight cycles. The mostly195.utim
functions the same way but has 171 in context instead of 195.
EIT: Cadence to be determined as allowed by the operations
team. Partial frame images would significantly increase the cross
calibration ability of the observer, especially in 171A, 195A and
284A. However, full disk observations in 171 or 195 would be
beneficial for co-alignment.
SXT: This instrument uniquely provides the higher temperature
analysis of these structures. The standard FFI table would be
appropriate. If the active region is not so active as to
overexpose the CCD on SXT a PFI table could be developed that
would visit the limb and briefly point at an appropriate
target. This could be accomplished by using the multi-OR
capability of SXT. If the loop region is large a 128x128 OR at
full-resolution will be sufficient. This should use sequential
exposures in Al.1, AlMg, and Al12 with automatic exposure
control. If the multi_OR is required the region must be observed
long enough for the AEC to settle. PFI images could follow the
same basic procedure with a 64x64 OR at full resolution. It is
important to note that although the structure may not be visible
in the SXT images, this to is an important null result.